As far as books in English are concerned, one should add the English translation of Petropoulos smaller opus: Songs of the Greek Underworld: The Rebetika Tradition, translated by Ed Emery who with the Rebetology Institute promotes the yearly Rebetika gathering in Hydra as well as the Famous Rebetika Band in London. Easy available on the net, and chock-full of interesting stuff. To be totally avoided is Rebetika: Music from the Old Greek Underworld (Black Rose Books) I bought it and it's a scam. The subject is fascinates and requires a lot of pleasant digging!